Abstract: Through thin section identification and mercury injection, in combination with logging data and formation water analysis, the study on the low resistivity oil layers from Xishanyao formation in east area of Xi'xiagou of Santanghu basin was carried out. The results indicate that the main lithology is lithic sandstone and feldspathic lithic sandstone, with lower compositional and texture maturity, the reservoir space is dominated by residual intergranular pores and dissolution inner pores, and the sedimentary environment plays a key role in the formation of low resistivity oil layers, which is mainly due to the massive distribution of siderite and pyrite and high formation water salinity.